This invention relates to edge card connectors and particularly to low insertion force edge card connectors for use in conjunction with printed circuit boards and edge cards. More particularly, this invention relates to an edge card connector having a plurality of preloaded, low insertion force electrical spring contacts.
Edge cards are a variety of printed circuit board generally designed to be mounted perpendicular with respect to a mother circuit board. Edge cards are often identified as daughter boards because of their relation to the mother boards on which they are mounted. The perpendicular mounting permits flexibility in circuit design, placement of a plurality of edge cards in electrical connection with a single mother circuit board, easy insertion or replacement of the edge card, and ease of fabrication of assemblies of edge cards and the mother circuit board.
Electrical connection between the edge card and the mother circuit board is maintained with the aid of an edge card connector that mechanically holds the edge card in a desired position, and provides an electrically conductive pathway between the edge card and the mother circuit board. Conventional edge card connectors such as disclosed in U.S. Pat. No. 3,530,422 to Goodman have socket-type mechanisms with non-preloaded electrical contacts fitted in a housing into which an edge card can be inserted or removed.
In many cases, insertion of edge cards into a socket type electrical edge connector can be difficult. Socket type edge connectors can include a socket contact having two electrically conductive spring-loaded arms that engage opposite sides of the edge card as it is inserted into the socket contact. These spring arms cooperate to clamp the edge card contact in place and ensure that the electrical connection between the card and the socket is not broken intermittently upon exposure of the assembly of edge card and edge card connector to shock, vibration, or other physical movement. Ordinarily, a significant clamping force must be exerted by the spring arms to provide an uninterrupted electrical contact between the edge card contact and the mating socket contact provided in the edge card connector. It will be understood that other clamping means, in addition to the socket contact, generally is provided in an edge connector for clamping the edge card to its mother board to hold the edge card in a stable position largely unaffected by shock or vibration.
Even though exerting somewhat high clamping forces against the edge card is desirable because the mechanical and electrical connection is maintained better at high clamping forces than at relatively lower clamping forces, it has been observed that high clamping force connections can make insertion of an edge card into a socket contact of an edge card connector difficult, particularly for automated equipment commonly used to insert edge cards into the edge card connector. Manual or automatic insertion that uses higher insertion forces to insert the edge card into the socket contact is not advisable, because of the increased chance of the damage to the edge card or the edge card connector if the edge card is misaligned during insertion.
The problems associated with high insertion forces can be alleviated by providing edge card connectors configured to require only low insertion forces for an edge card. For example, U.S. Pat. No. 3,671,917 to Ammon et al. and U.S. Pat. No. 3,737,838 to Mattingly, Jr. are examples of low insertion force edge card connectors that preload two spring arms that act as electrical contacts. A preload tab is positioned at the terminal end of the spring arms to engage a portion of an insulative housing so that the insertion forces required are diminished.
It is therefore an object of this invention to provide an edge card connector requiring low insertion forces to insert an edge card that is still capable of maintaining a high normal force to engage and clamp an edge card sufficiently to establish an electrical connection between the edge card and the connector.
It is a further object of this invention to provide a low insertion force edge card connector having an insulative housing in which an electrical conductor is configured to form a spring that is preloaded by engagement with the insulative housing to minimize the insertion force and that is displaced by an edge card during insertion to exert a normal force against the contact surface of the edge card to maintain an electrical contact between the edge card and the edge card connector.
Yet another object of this invention is to provide an insertion tool for use in conjunction with a socket contact to assist in installing the socket contact in an insulative housing to form an edge card connector requiring low insertion forces to insert an edge card.
Still another object of the present invention is to provide a tool that is insertable into an insulative housing of an edge card connector to support the insulative housing during insertion of a socket contact into the insullative housing and also to maintain the spring arms of the socket contact in a spread or splayed configuration until preloading tabs on the spring arms engage flanges provided in the insulative housing to lock the spring arms in a preloaded position.
One further object of the invention is an assembly of a socket contact including a spring having a low spring rate compactly fitted into a housing, and having a preload tab extending from a junction between the spring arm and the contact arm.
In accordance with the foregoing objectives, an apparatus for forming a low insertion force connector for edge cards includes an insulative housing having a support mount for supporting an edge card. The support mount has a primary camming surface along which socket contacts can slide as they are inserted into a cavity formed in the insulative housing. Also included in the housing is a preload block or flange situated above and to the left of the support mount. Another component of the apparatus is an insertion tool having an auxiliary camming surface that is aligned with the primary camming surface of the support mount to provide continuous means for camming the spring arms of the socket contact to a spread-apart, preloaded position cocked to engage the preload block upon full insertion of the socket contact into its cavity in the insulative housing.
During emplacement of a socket contact into the insulative housing, each spring arm slidably moves along the camming surfaces of first the support member and subsequently the insertion tool. The socket contact includes a spring arm attached to the housing and a contact arm integrally appended to the distal end of the spring arm. The contact arm contacts the first camming surface during insertion of the socket contact into the insulative housing so that the spring arm is moved outwardly during insertion of the socket contact into the housing, permitting a preload tab, appended to the socket contact at the junction between the spring arm and contact arm to engage the preload block, and thereby maintain the spring arm under springing tension having a force component directed normal to an edge card inserted into the housing so that force is transmitted to the edge card by the contact arm.
In preferred embodiments, the socket contact is configured to form a double armed spring with first and second contact surfaces between which the edge card is clamped by spring forces exerted normal to the surface of the edge card to ensure steady maintenance of electrical contact. Attachment of the socket contact to the support mount on the edge connector housing is enabled by a first and second clamping portion that clamps the socket contact to the support mount in locking engagement. These first and second clamping portions are formed at the proximal end of the two spring arms appended to the solder tail of the socket contact. Barbed catches are formed on the first and second clamping portions to cause the clamping portions to be coupled permanently to the support mount.
The preload tabs are situated at a junction between the proximal end of the contact arms and the distal end of the spring arms. The preload tabs are protruding tabs that extend away from the spring arms to engage preload blocks attached or integrally formed with the insulative housing. Engagement of the tabs and the preload blocks acts to separate the contact arms in spread apart or splayed relation and consequently preload the spring arms, which are maintained under greater springing tension then an equivalent spring lacking preload tabs that is similarly positioned in the housing.
An advantage of preloaded spring arms is the reduced insertion force necessary to insert an edge card into the edge card connector. The contact surfaces of the contact arms are curved to provide a ramping or wedging surface against which an edge card that is being inserted can act against in order to force the spring arm outward from the edge card. If the wedging surface is canted at a high angle relative to the inserted edge card, the static and dynamic frictional forces are quite high, and the component force exerted normal to the edge card to move the contact arm outward is greatly reduced relative to those wedging surfaces positioned nearly parallel to the surface of the inserted edge card. These problems can be greatly reduced by preloading the spring arms so that the spring arm is held under tension in a position that still ensures the application of high normal forces to a fully inserted edge card, yet also presents a contact surface lying nearly parallel to the surface of the edge card as the edge card is inserted into the edge card connector. This positioning greatly reduces the insertion force required to overcome the static and dynamic frictional forces between the edge card and the contact surface, and greatly eases the force required to move the contact arm outward.
Another advantage is provided by constructing the electrical connector with an insertion tool to form an auxiliary camming surface along which the contact surfaces of the contact arms can slide during insertion of the spring arms into the housing. The insertion tool temporarily forms a camming surface in conjunction with the camming surface of the supporting mount and acts to spread the spring arms and thereby guide the preload tabs into their proper working position. Without the insertion tool, the spring arms would not be placed under an outward tension that spreads the contact arms far enough apart and moves the preload tabs into a spread position suitable for engaging the preload blocks. No complex features or guides are required on either the spring arms or the housing to guide the preload tabs into the proper operating position.
Yet another advantage of the present invention is provided by the wiping action of the contact surfaces as the edge card is inserted. In contrast to simple cantilever springs, the serpentine configuration of the the spring arm permits the spring arms to move essentially parallel to the surface of the edge card during insertion. This essentially parallel movement increases the area of the surface of the edge card wiped clean of debris that could reduce the electrical contact between the contact surface of the contact arm and the edge card.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art on consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.